DISCLAIMER: I have not read all the posts... nor will I.
What should YOU offer for the boat?: $0 - you don't want it, so don't buy it.
What can you do?: Help him/her/them sell it, by offering them sound objective advise.
I would suggest the following:
They should ask $8K for the boat with the motor (good luck)
Or, try to sell the motor alone for $2K, and the boat for $6K. The money that they spent on depth, speed instruments, cushions, main-sheet blocks running rigging etc. may help them sell faster, but they will not likely recoup it...
Do not buy a boat as a financial investment, but rather an investment in yourself.